IMPACT OF MICROBIAL AND PHYSICO-CHEMICAL QUALITIES OF TREATED WASTEWATER EFFLUENT ON
RECEIVING WATER BODIES IN DURBAN
SHALINEE NAIDOO
Submitted in fulfilment of the academic requirements for the degree of Master of Science (MSc) in the Discipline of Microbiology; School of Life Sciences; College of Agriculture, Engineering and Science at the University of KwaZulu-Natal, Durban.
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“We have lived our lives by the assumption that what was good for us would be good for the world. We have been wrong. We must change our lives so that it will be possible to live by the contrary assumption, that what is good for the world will be good for us. And that requires that we make the effort to know the world and learn what is good for it.”
- Wendell Berry
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ACKNOWLEDGEMENTS
Professor A. O. Olaniran for his endless guidance, constant support and encouragement. Without your supervision, this would not have been possible. Thank you.
Professor B. Pillay for his guidance, support and encouragement.
Professor M. Taylor for her guidance with viral recovery and detection.
National Research Foundation (NRF) for financial support.
Medical Research Council for financial support.
Basil Naidoo for his time and assistance.
Mnqayi Wisemen Sakhi and Bewu Gambana for their time and help during samplings.
The Erasmus Mundus SAPIENT Scholarship Program and Radboud University Nijmegen for providing me with the opportunity to study abroad.
The Water Research Group of Lab 4 for bringing the entire research project together. May we never stop in our fight to save mankind’s precious resource.
“Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. ”
- Margaret Mead
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ACKNOWLEDGEMENTS
My parents – without your constant guidance and never ending support, this would not have been possible. You have shown me that with passion and hard work, I can achieve anything. To my father, Sagaran Naidoo – thank you for your constant help during monthly samplings and with construction of the viral recovery system. To my mother, Krishnee Naidoo – thank you for all your support and advice and for travelling 9364 kilometers to ensure I was okay.
“If I have seen further than others, it is by standing upon the shoulders of giants”
- Isaac Newton
My sister - Jineshnee Naidoo - Thank you for always being there for me and taking the time to understand the true meaning of PCR and DGGE. This journey has been a long one but there is no one else who I'd rather have by my side when I lose my wallet in Barcelona, leave my iPod on the train in London or break my glasses in Nijmegen. Here's to the amazing things past and to the wonderful things which the future holds. May our bond always stay strong.
Deseree Alvika Rajpal – we have come a long way – from weighing soil, collecting wastewater, failed PCR’s and Real Time troubleshooting. Late nights in the lab, googling random theories, finally understanding the Mauna Loa curve and of course, travelling across Europe and exploring the world. This has been a long journey which would not have been possible without you. These five lines will never be able to express a thank you big enough for being more than a friend and always knowing the right thing to say. May we never forget the last two years.
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Ashmita Arjoon and Sphephile Nzimande – In you, I have found more than friendship, it is a sisterhood bound by the warmth of endless lattes and conversations about life. Thank you for your constant words of encouragement, support, advice and help throughout this study.
To my international colleagues and friends of Radboud University Nijmegen and The Erasmus Mundus SAPIENT Scholarship Program – behind every great achievement is an amazing story and my time abroad is testament to that. It has been one of the most enriching experiences for both my personal and academic career, allowing me to grow into a more free- thinking, independent member of society. I will always hold these six months close to my heart.
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LIST OF FIGURES
Figure 1.1: Overview of treatment stages within a wastewater treatment plant (adapted from AWA, 2009;
UNEP, 2012). 7
Figure 1.2: Transmission routes of human enteric viruses (adapted from WHO, 1979; Gerba et al., 1975;
Bosch et al., 2006). 32
Figure 2.1: Map of study area showing major sampling points. 47
Figure 2.2: Images illustrating various activities noted during samplings: A: overflow from broken pit latrine toilets (Upstream Aller River); B: Informal settlements located on the banks of the Aller River; C: Discharge of domestic waste from surrounding rural settlements (Upstream Aller River); D: Excessive red larvae (Aller River); E: Discharge of poorly treated effluent at NWWTP; F: Poor chlorine treatment within the NGTW. 48
Figure 2.3: Monthly variations of salinity and rainfall for the Umgeni River between March 2012 –
February 2013. 53
Figure 2.4: Monthly variations of salinity and rainfall for the Aller River between March 2012 –
February 2013. 53
Figure 2.5: Monthly variations of turbidity, BOD and TSS of the NWWTP treated effluent and the receiving Umgeni River over the sampling period. Bars indicate the average of replicate samples (n = 3) whilst error bars show standard deviation. Turb: Turbidity; BOD: Biological Oxygen Demand; TSS: Total Suspended Solids; BC: Before Chlorination; DP: Discharge Point; US: Upstream; DS: Downstream. 57
Figure 2.6: Monthly Variations of Turbidity, BOD and TSS of the NGTW treated effluent and the receiving Aller River over the sampling period. Bars indicate the average of replicate samples (n = 3) whilst error bars show standard deviation. Turb: Turbidity; BOD: Biological
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Oxygen Demand; TSS: Total Suspended Solids; BC: Before Chlorination; DP: Discharge Point; US: Upstream; DS: Downstream. 58 Figure 2.7: Monthly variations of Nitrate, Phosphate, Residual Chlorine and Sulphate concentrations of the effluent samples collected from the NWWTP and Umgeni River over the sampling period. Bars indicate the averge of replicate samples (n = 3) whilst error bars show the standard deviation. NO3: Nitrate; PO4: Phosphate; Cl2: Residual Chlorine; SO4: Sulphate;
BC: Before Chlorination; DP: Discharge Point; US: Upstream; DS: Downstream. 60
Figure 2.8: Monthly variations of Nitrate, Phosphate, Residual Chlorine and Sulphate concentrations of the effluent samples collected from the NGTW and Aller River over the sampling period.
Bars indicate the average of replicate samples (n = 3) whilst error bars show the standard deviation. NO3: Nitrate; PO4: Phosphate; Cl2: Residual Chlorine; SO4: Sulphate; BC: Before Chlorination; DP: Discharge Point; US: Upstream; DS: Downstream. 61
Figure 3.1: Presumptive E. coli (EC), faecal coliform (FC), faecal streptococci (FS) and enterococci (ENT) load in NWWTP effluent detected at the before chlorination (BC) and at discharge point after chlorination (DP) between March 2012 and February 2013. All bars represent average (n=3) values ± standard deviation. 86
Figure 3.2: Presumptive E. coli (EC), faecal coliform (FC), faecal streptococci (FS) and enterococci (ENT) population detected upstream (US) and downstream (DS) of the Umgeni River between March 2012 and February 2013. All bars represent average (n = 3) values ± standard deviation at a CFU/ml as indicated however E.coli population detected downstream during August 2012 is represented as x104 CFU/ml. 87
Figure 3.3: Presumptive E. coli (EC), faecal coliforms (FC), faecal streptococci (FS) and enterococci (ENT) load detected in NGTW before chlorination (BC) and at the discharge point after chlorination (DP) between March 2012 and February 2013. All bars represent average (n=3) values ± standard deviation at a CFU/ml as indicated. 88
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Figure 3.4: Presumptive E. coli (EC), faecal coliform (FC), faecal streptococci (FS) and enterococci (ENT) populations detected upstream (US) and downstream (DS) of the Aller River between March 2012 and February 2013. All bars represent average (n = 3) values ± standard deviation at a CFU/ml as indicated however E.coli population detected downstream during August 2013 as well as all indicators detected during September 2013 are represented as x103 CFU/ml. 89
Figure 3.5: Total coliform (TC) and total heterotrophic bacterial (THB) population enumerated before chlorination (BC) and after chlorination (AC) at the NWWTP as well as upstream (US) and downstream (DS) of the Umgeni River between March 2012 and February 2013. Values represent averages (n = 3) ± standard deviation at a CFU/ml as indicated, however, the total coliform population detected downstream during August 2012 is represented as x104 CFU/ml. 90
Figure 3.6: Total coliform (TC) and total heterotrophic bacterial (THB) population enumerated before chlorination (BC) and after chlorination (AC) at the NGTW as well as upstream (US) and downstream (DS) of the Aller River between March 2012 and February 2013. Values represent averages (n = 3) ± standard deviation at a CFU/ml as indicated however the total coliform population detected upstream (US) during August 2012 is represented as x103
CFU/ml. 91
Figure 4.1: Set-up for the recovery of human enteric viruses using a glass-wool adsorption elution
method (Van Heerden et al., 2005). 112
Figure 4.2: Evolutionary relationships of enteroviral taxa sequenced from NWWTP and receiving Umgeni River over all seasons. The evolutionary history was inferred using the Neighbour- Joining method (Saitou and Nei, 1987). The bootstrap consensus tree inferred from 500 replicates is taken to represent the evolutionary history of the taxa analysed. Branches corresponding to partitions reproduced in less than 50% bootstrap replicates are collapsed.
The percentage of replicate trees in which the associated taxa clustered together in the
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bootstrap test (500 replicates) are shown next to the branches (Felsenstein, 1985). The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Jukes-Cantor method (Jukes and Cantor, 1969) and are in the units of the number of base substitutions per site. The analysis involved 12 nucleotide sequences. Codon positions included were 1st+2nd+3rd+Noncoding. All positions containing gaps and missing data were eliminated. There were a total of 60 positions in the final dataset. Evolutionary analyses were conducted in MEGA5 (Tamura et al., 2011). 121
Figure 4.3: Evolutionary relationships of enteroviral taxa sequenced from NGTW and receiving Aller River over all seasons. The evolutionary history was inferred using the Neighbour-Joining method (Saitou and Nei, 1987). The bootstrap consensus tree inferred from 500 replicates is taken to represent the evolutionary history of the taxa analysed (Felsenstein, 1985).
Branches corresponding to partitions reproduced in less than 50% bootstrap replicates are collapsed. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (500 replicates) are shown next to the branches. The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Jukes-Cantor method and are in the units of the number of base substitutions per site (Jukes and Cantor, 1969). The analysis involved 13 nucleotide sequences. Codon positions included were 1st+2nd+3rd+Noncoding. All positions containing gaps and missing data were eliminated.
There were a total of 64 positions in the final dataset. Evolutionary analyses were conducted
in MEGA5 (Tamura et al., 2011). 122
Figure 4.4: Evolutionary relationships of adenoviral taxa sequenced from NWWTP and receiving Umgeni River over all seasons. The evolutionary history was inferred using the Neighbour- Joining method (Saitou and Nei, 1987). The bootstrap consensus tree inferred from 500 replicates is taken to represent the evolutionary history of the taxa analysed (Felsenstein, 1985). Branches corresponding to partitions reproduced in less than 50% bootstrap replicates are collapsed. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (500 replicates) are shown next to the branches. The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Jukes-Cantor method and are in the units of the number of base substitutions per site (Jukes
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and Cantor, 1969). The analysis involved 8 nucleotide sequences. Codon positions included were 1st+2nd+3rd+Noncoding. All positions containing gaps and missing data were eliminated. There were a total of 79 positions in the final dataset. Evolutionary analyses were conducted in MEGA5 (Tamura et al., 2011). 123
Figure 4.5: Evolutionary relationships of adenoviral taxa sequenced from NGTW and receiving Aller River over all seasons. The evolutionary history was inferred using the Neighbour-Joining method (Saitou and Nei, 1987). The optimal tree with the sum of branch length = 0.22952000 is shown. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (500 replicates) are shown next to the branches (Felsenstein, 1985). The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Jukes-Cantor method and are in the units of the number of base substitutions per site (Jukes and Cantor, 1969). The analysis involved 4 nucleotide sequences. Codon positions included were 1st+2nd+3rd+Noncoding. All positions containing gaps and missing data were eliminated. There were a total of 96 positions in the final dataset. Evolutionary analyses were conducted in MEGA5 (Tamura et al., 2011). 123
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LIST OF TABLES
Table 1.1: Overview of various secondary treatment options available 9
Table 1.2: Overview of treatment requirements for selected effluent discharges Adapted from Wastewater Treatment Guidance Manual – Syrian Lebanese Higher Council (2012) 18
Table 1.3: Pathogens associated with waterborne diseases and sources of contamination (adapted from
Grabow et al. (2001) 20
Table 1.4: Currently used guidelines by the eThekwini Municipality (South Africa) for treated effluent being discharged into an receiving catchment. Adapted from Government Gazette, 1984; (A):
Guidelines for effluent being discharged into any area other than that specified by B. (B):
Guidelines for effluent being discharged into any catchment area/ river or a tributary
29
Table 1.5: Microbial contaminants on the United States Environmental Protection Agency Contaminant
Candidate List (adapted from USEPA, 2012) 34
Table 1.6: Examples of waterborne viruses detected from various sites and common methods used for their
detection 36
Table 2.1: Major operational areas for the NWWTP and NGTW. Adapted from The Greendrop Handbook
(DWA, 2012) 45
Table 2.2: Physicochemical profiles of treated effluents of the NWWTP and its receiving watershed over the sampling period. Results Represent Averages ± Standard Deviation. G: Guideline for treated effluent (Government Gazette, 1984); T: Temperature; TDS: Total Dissolved Solids;
DO: Dissolved Oxygen; COD: Chemical Oxygen Demand; EC: Electrical Conductivity; SAL.:
Salinity; RES.: Resistivity 54
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Table 2.3: Physicochemical profiles of treated effluents of the NGTW and its receiving watershed over the sampling period. Results Represent Averages ± Standard Deviation. G: Guideline for treated effluent (Government Gazette, 1984); T: Temperature; TDS: Total Dissolved Solids;
DO: Dissolved Oxygen; COD: Chemical Oxygen Demand; EC: Electrical Conductivity;
SAL.: Salinity; RES.: Resistivity 55
Table 2.4: Correlation matrix between the physico-chemical parameters obtained for the NWWTP effluent and receiving Umgeni River. T: Temperature; TURB: Turbidity; TSS: Total Suspended Solids; DO: Dissolved Oxygen; BOD: Biological Oxygen Demand; COD:
Chemical Oxygen Demand; EC: Electrical Conductivity; SAL: Salinity; RES: Resistivity;
HPC: Heterotrophic Plate Count; TC: Total Coliforms 62
Table 2.5: Correlation matrix between the physico-chemical parameters obtained for the NGTW effluent and receiving Aller River. T: Temperature; TURB: Turbidity; TSS: Total Suspended Solids;
DO: Dissolved Oxygen; BOD: Biological Oxygen Demand; COD: Chemical Oxygen Demand; EC: Electrical Conductivity; SAL: Salinity; RES: Resistivity; HPC: Heterotrophic Plate Count; TC: Total Coliforms 63
Table 3.1: Outline of the respective media and incubation conditions used for the enumeration and identification of each bacterial indicator (Standard methods, 1998) 80
Table 3.2: Coliphage counts for all samples collected for the NWWTP and receiving Umgeni River 93
Table 3.3: Coliphage counts for all samples collected for the NGTW and receiving Aller River 94
Table 3.4: Correlation matix between physicochemical and microbial parameters for the NWWTP and Umgeni River. T: Temperature; TURB: Turbidity; TDS: Total dissolved solids; TSS: Total Suspended Solids; pH; DO: Dissolved Oxygen; BOD: Biological Oxygen Demand; COD:
Chemical Oxygen Demand; SAL: Salinity; FC: Faecal Coliforms; FS: Faecal Streptococci;
ENT: Enterococci; TC: Total Coliforms; THB: Total Heterotrophic Bacteria 96
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Table 3.5: Correlation matix between physicochemical and microbial parameters for the NGTW and Aller River. T: Temperature; TURB: Turbidity; TDS: Total dissolved solids; TSS: Total Suspended Solids; pH; DO: Dissolved Oxygen; BOD: Biological Oxygen Demand; COD:
Chemical Oxygen Demand; SAL: Salinity; FC: Faecal Coliforms; FS: Faecal Streptococci;
ENT: Enterococci; TC: Total Coliforms; THB: Total Heterotrophic Bacteria 97
Table 4.1: PCR Primers used for the detection of Enteroviruses and Human Adenoviruses 116
Table 4.2: Seasonal detection of human adenovirus and enterovirus in water samples collected from the NWWTP and NGTW and receiving Rivers. BC: Before chlorination; DP: discharge point;
US: upstream; DS: downstream; (+): virus present; (-): no virus detected 119
xii ABSTRACT
Increase in magnitude of the global freshwater crisis together with the constantly changing demographics, hydrological variability and rapid urbanization will allow for continuous over exploitation of existing water resources, in an attempt to satisfy the rising socioeconomic demands. Increasing pressure on existing wastewater treatment plants, together with inefficient hygiene practices have exacerbated the nutrient and microbiological loads constantly entering surrounding water systems. This, coupled with the use of outdated guidelines has resulted, not only in an increase in waterborne related diseases but also an increase in waterborne-disease-related deaths. The current study investigated the physicochemical and microbiological quality of treated effluent from two independent wastewater treatment plants as well as their impact on the receiving watershed within Durban, South Africa over a one year period.
Microbiological and physicochemical profiles were determined using standard methods whilst conventional PCR was used for the seasonal detection of human enteric viruses. Monthly variations were observed for all parameters with eight and six out of 12 month samples exhibiting increases in turbidity at the discharge point for the NWWTP and NGTW respectively, relative to before chlorination. Similarly, increases in nitrate and phosphate levels at the discharge point were also noted with the highest being recorded during December (215.23%) and September (12.21%) respectively. Temperature profiles ranged between 12 – 26 °C and 12.7 – 26 °C for the NWWTP and receiving Umgeni River whilst for the NGTW and receiving Aller River, it ranged between 16.5 – 26 °C and 12 – 25.7 °C respectively. Seasonal averages revealed relatively high COD values downstream of the Umgeni River during winter (263.22 mg/l) and spring (177.93 mg/l). Eight out of twelve samples exhibited increases in turbidity at the discharge point for the NWWTP with the highest values obtained during April (76.43 NTU). Significant positive correlations (p ≤ 0.05) were observed upstream and downstream of the Umgeni River between temperature and BOD (r = 0.624); turbidity (r = 0.537); TDS (r = 0.437); TSS (r = 0.554) and DO (r = 0.516). Percentage reduction of bacterial indicators at the discharge point ranged between 0.52 – 100%
and 41.56 – 100% across the sampling period for the NWWTP and NGTW, respectively. Treated effluent from both plants did not meet the required guidelines, with a 100% reduction in the faecal coliform load
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being detected only during October 2012 for both plants. In addition, higher levels of indicator bacteia were observed at the discharge point for the NWWTP during February 2013 with observed counts (in CFU/ml) as high as 12.27 x 103; 6.61 x 103; 2.99 x103; 1.6 x 103 and 1.17 x103 for total coliforms, E.coli, faecal coliforms, faecal streptococci and enterococci, respectively. Similarly, higher levels of both somatic and F-RNA bacteriophages were detected during April (106.67 PFU/ml), May (309.33 PFU/ml).
June (346.67 PFU/ml) and August (126.67 PFU/ml) compared to samples collected before chlorination for the NWWTP. Enteroviruses were detected in 100% of unchlorinated final effluent samples, 87.5% of chlorinated final effluent and 93.75% of receiving river samples whilst human adenoviruses were detected in 50% of final effluent samples before chlorination, 62.5% in samples collected at the discharge point and 62.5% of river water samples. This study revealed that whilst the independent treatment plants monitored, exhibited effluent qualities that met acceptable standards for some parameters such as pH and temperature, the effluent quality fell short of other standard requirements. Ensuring efficient surveillance and management of existing treatment plants coupled with guideline revision and monitoring compliance is imperative in preventing further risk of pollution to both the environment and human health.
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CHAPTER ONE
INTRODUCTION AND LITERATURE REVIEW
1.1 Introduction
Safe drinking water and proper sanitation have constantly been recognized as indispensable factors to sustain life. The magnitude of the global freshwater crisis is underestimated, with many people struggling to have access to safe water which is a critical natural resource upon which all socio-economic development and ecosystem functions depend. The importance of this finite resource was further stressed at the Bonn 2011 Conference amongst both energy and food security issues in conjunction with The Rio+20 Summit (2012) indicating water as a major critical player in sustaining a Green Economy (Jägerskog and Clausen, 2012). According to the World Health Organization (WHO), approximately one billion people, worldwide, lack access to adequate water supplies. Furthermore, despite constant progress towards reaching the Millennium Development Goals (MDG) it is already known that the world lags behind on the sanitation target with an additional 1 billion people still lacking adequate sanitation facilities (Bigas, 2012). This crisis is further compounded by factors such as increasing poverty, accelerated population growth and rapid urbanization coupled with hydrological variability and climate change. In mid-lateral developing countries, access to clean water and sanitation are a luxury, with constant national, international and trans-boundary conflicts arising in an attempt to provide adequate food, water and health security for entire populations, thus hindering any developmental progress (WWAP, 2012). These socio-economic and environmental factors place even further stress on the deteriorating water and sanitation infrastructure, more so in developing
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regions, where billions are still at risk of Water, Sanitation and Hygiene (WaSH) related diseases (GLAAS, 2012).
Despite meeting the MDGs regarding access to potable water, the depletion of existing finite water resources still continues to be a major problem, with projections that approximately 605 million people will still lack access to improved drinking water by 2015 (UNICEF/WHO, 2012).
In addition, the lack of access to potable water is estimated to cost countries between 1 – 7% of their annual GDP, with slow water and sanitation-related progress further impeding national economic growth (GLAAS, 2012). This together with the above named factors serve as the major driving force behind the increased use of wastewater, surrounding surface water and grey water for various recreational, agricultural and aqua-culture activities (WHO, 2011a). In addition, the mortality of global water-associated diseases exceeds 5 million people annually with approximately 50% arising from microbial intestinal infections (Cabral, 2010). In 2008, Stockholm’s International Water Institute estimated that approximately 1.4 billion people live in closed basins which are defined as regions where a range of agricultural, industrial, municipal and environmental needs cannot be met by existing water supplies. In 2007, The United Nations Food and Agriculture Organization (FAO) estimated that 1.2 billion people live in water scarce countries, with population numbers expected to rise to 1.8 billion by 2025, thus further increasing the number of countries and regions that would experience a water scarcity problem (Water Industry Market, 2010). These projected increasing demographics have resulted in a constant competition with the environment for currently diminishing water resources and together with an increasing number of rivers no longer reaching the ocean, the rate of surface and groundwater contamination has greatly increased (GLAAS, 2012).
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Reliable wastewater treatment systems serve as a good indicators of the level of development within a municipality as well as community health, with the degree and quality of treated wastewater determining the impact of these treatment plants on surrounding water sources into which it is released (DWA, 2011). Over the last few years, the quantity of municipal wastewater produced has drastically increased due to the constant increase in population numbers together with an increased dependence on diminishing water resources. This coupled with the discharge of inefficiently treated wastewater into surrounding surface water sources serve as a direct threat, not only to the macro- and micro-flora and fauna present but also to the greater provision of good quality water required for all socio-economic functions. Thus, the constant monitoring of the operational status of existing wastewater treatment plants (WWTPs) as well as increasing emphasis on environmental and water resource health have become key factors in determining the quantity and quality of wastewater generated by respective municipalities.
Most waterborne diseases result from some form of faecal pollution. In order to ensure the protection of current and future water resources, organisms such as coliforms, E. coli, Clostridium, Enterococci and Faecal Streptococci which serve as indicators of contamination, are used to assess water quality. Testing for individual pathogens would be impractical and expensive due to extensive analytical costs as well as various technical difficulties associated with detecting certain pathogens generally present in low quantities and chemically complex environments (DWAF, 1996a). This in conjunction with various legally enforceable standards, guidelines and target water quality ranges have been set in order to ensure that these contaminants do not exceed the minimal infectious dose in order to prevent severe disease outbreaks and extensive damage to surrounding environments (Barrell et al., 2000). Previous studies have shown counts of coliform bacteria excreted from the human gut ranging between
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100 – 400 billion counts per day, raising a high degree of concern with diseases related to human waste. Due to a large degree of waterborne diseases being transmitted as a result of human- contaminated water sources, the absence of coliform indicator bacteria is usually taken as an indication that the sample is free of pathogenic microorganisms (WHO, 2003a).
1.2 Sources of domestic and industrial wastewater
Wastewater is defined as any clear water, storm water, industrial, domestic or commercial sewage or any combination thereof carried by water (EPA, 2007). Several types of sewage have been nationally defined by the Consortium of Institutes for Decentralized Wastewater Treatment (CIDWT, 2009) based on sewage source components; namely black water; grey water and yellow water. The type and volume of wastewater generated is determined by both, the population numbers and the combination of surrounding domestic, recreational and industrial activities, all of which affect discharge patterns as well as the chemical status of the treated effluent. In order to set up an efficient waste management system, proper identification and characterization of the influent entering a wastewater treatment plant is essential (Mara, 2004).
This is based on the physical, chemical and biological characteristics of the influent; the quality required for maintaining the surrounding environment into which the wastewater will be discharged as well as the current environmental and discharge standards.
Four main types of wastewater have been identified namely domestic, industrial, agricultural and urban. Generally, the focus is mainly on domestic and industrial sewage as a source of plant influent and contamination, however agricultural runoff is now becoming increasingly important due to the high quantities of pesticides and fertilizers being used, ultimately contributing to
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surface water eutrophication (DWA, 2011). Domestic wastewater is defined as sewage which generally consists of black water composed of fecal matter (human and animal wastes) together with grey water, composed of wastewater sources originating from a range of household activities (washing and bathing) with each forming approximately 32.5% and 67.5% of domestic sewage respectively (EPA, 2007). Initially, this water is used for drinking, food preparation, hot water systems, bathing and personal hygiene, washing, gardening and may ultimately form part of the domestic wastewater being excreted into the environment (DWAF, 1996a). Within a household, individual domestic wastewater streams all contribute different amounts to the overall nutrient and elemental load contained in the discharged effluent. Industrial wastewater however, is defined as sewage consisting of industrial wastes such as pulp, paper, petrochemical runoff as well as various chemicals, salts and acids. These sources vary widely in composition and often require special tertiary treatment in order to comply with discharge regulations. The composition of industrial wastewater varies based on the type of surrounding industry together with the respective contaminant and pollutant composition with general classification into inorganic or organic industrial wastewater (Rosenwinkel et al., 2005).
1.3 Overview of steps involved in wastewater treatment
Initially, all wastewater was discharged directly into natural waterways, where a dilution effect would occur in conjunction with the degradation of organic matter by existing microorganisms.
However, due to the constant increase in population numbers and densities, as well as an increase in the production of both domestic and industrial waste, the pollution of surrounding environments and deterioration of public health has escalated. This resulted in the need to
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introduce WWTPs that would aid and accelerate the purification process prior to discharge into any natural waterway (USEPA, 2004). In addition, provided that these plants operate efficiently, the treated wastewater effluent and sludge produced could serve as a valuable resource when safely reused. The overall wastewater treatment process can be broken down into four main stages namely the pretreatment, primary, secondary and tertiary stages (Figure 1.1).
1.3.1 Pretreatment
The first stage of treatment involves the use of screens to remove larger debris such as paper, plastic or any other foreign material which may damage downstream equipment, followed by further removal of grit and silt which may be harmful to plant equipment. In addition, the screened materials are often hazardous and must be safely disposed off to prevent fly breeding, excessive odours or downstream hazardous effects to public and environmental health. One such suitable disposable method is deposition in trenches covered with soil. In addition, the incineration of solids prior to burial is often preferred (DWA, 2011). Excess grit such as sand, silt and stones can cause severe operational problems, affecting a range of subsequent treatment steps, ultimately causing severe pump blockages. Grit removal is therefore essential to protect mechanical equipment and pumps from abrasion and to reduce blockages. In addition measuring daily flows within a plant to ensure the maintenance of functional capacity is imperative in producing effluent of good quality (Sonune and Ghate, 2004).
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Figure 1.1: Overview of treatment stages within a wastewater treatment plant (Adapted from EPA, 1997; UNEP, 2012)
1.3.2 Primary treatment
The main purpose of primary treatment is to reduce any settleable solids, as well as oils, grease, fats, sand and grit within the wastewater via settling and sedimentation processes. The steps involved in primary treatment are entirely mechanical by means of filtration and sedimentation (Sonune and Ghate, 2004). After initial screening to remove larger debris, wastewater still contains dissolved organic and inorganic constituents as well as suspended solids which are removed via the process of primary settling, sedimentation, chemical coagulation or filtration.
SECONDARY CLARIFIER
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This allows for separation of the solid and liquid phases in the wastewater by removing those settled organic solids as well as any floating materials such as fats, oil and grease. Wastewater enters a sedimentation tank, where the flow rate gradually slows down, enabling the wastewater to sit in these settling tanks which have been designed to hold the wastewater for several hours, during which, most of the heavy solids sink to the bottom of the tank, forming primary sludge which reduces the suspended solid content of the wastewater. In addition, any surface floating materials is usually siphoned off (USEPA, 2004).
1.3.3 Secondary treatment
Following primary treatment, wastewater flows into the next stage whereby the remaining suspended solids are decomposed and the microbial load is greatly reduced. A variety of secondary treatment options are available (Table 1.1) which are classified into three main categories, namely, wastewater stabilization ponds, suspended growth systems or fixed film systems ultimately resulting in an organic matter removal of approximately 90%. Wastewater stabilization ponds may be constructed either singularly or in parallel with the number of ponds increasing as the volume of waste being processed by the plant increases. These ponds are classified by the type of bacteria responsible for the decomposition process as well as the duration for which the waste will remain in the pond (Mara, 2004). On the other hand, suspended growth systems are generally applied to smaller communities and consist of 3 main types:
activated sludge, sequential batch reactor and aerated lagoons whilst fixed film systems involve the passage of raw wastewater onto a filter medium to which bacteria can attach, build up and accumulate in biomass which is subsequently removed.
9
Table 1.1: Overview of various secondary treatment options available
TREATMENT DESIGN CRITERIA EFFLUENT
QUALITY
ADVANTAGES DISADVANTAGES REF
WASTE STABILISATION PONDS Anaerobic ponds 2 - 5 m deep, pH usually below 6.5; less
surface area; covered either by gravel, plants, steel, and plastic. Loaded at high
rates to prevent inlet of any oxygen
BOD Removal of 60 - 85%
Low cost, little excess sludge produced, Small pond volume needed; Low nutrient requirements;
Low operating costs; no electricity required; Methane by-product
Requires more land; Long start-up required, can produce an unpleasant
odour; Requires sludge removal more often; Operates optimally at
warmer temperatures (>25 °C)
Alexiou and Mara, (2003);
Norton et al., (2012)
Facultative ponds
Shallow – 1-3 m deep; Length to breadth ratio should be a minimum of 2:1; lined with
compact clay (minimum thickness 0.3 m) or polyethylene; formation of two layers - aerobic at surface and anaerobic at bottom
BOD removal of 70 - 85%
Efficient BOD reduction; Nutrient reduction by aerobic and anaerobic
bacterial processes as well as by surrounding plants; Natural aeration
of the upper layer via movement of air; Low energy consumption
Significant space requirements;
Efficiency is strongly affected by environmental factors; continuous
maintenance required
Norton et al., (2012)
Maturation ponds (polishing ponds)
Shallow – 0.9 - 1 m deep; allows for light penetration; completely aerobic; high pH and high concentration of dissolved oxygen
due to algal activity; little biological stratification; size and number depends on
required effluent pathogen concentration
Little BOD removal because most has
been removed in previous stages
Removes excess nutrients and pathogens such as faecal coliforms
Small BOD removal; additional costs; additional land requirements
Norton et al.
(2012)
SUSPENDED GROWTH SYSTEMS Activated sludge Oxygen supplied for initial sludge
decomposition and provide agitation to promote flocculation; 85% sludge removed
whilst 15% recirculated
BOD removal of 90 - 98%
Production of high quality effluent;
reasonable operational and maintenance costs;
High capital costs; high energy consumption; regular monitoring
required; back washing needed
Batch reactor Equalization, biological treatment and secondary clarification are performed in a single reactor vessel using a timed control sequence; aeration may be provided by
bubble diffusers/floating aerators
BOD removal of 89 - 98%
Initial capital cost savings; all processes carried out in a single
reactor vessel; timed cycles;
requires limited land; equalization of processes
Higher level of sophistication and maintenance required as timing must be controlled; may discharge settled or floating sludge; clogging
of aeration devices; requires oversized outfalls as effluent
discharge is timed
USEPA, (1999a); Mahvi
(2008)
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TREATMENT DESIGN CRITERIA EFFLUENT
QUALITY
ADVANTAGES DISADVANTAGES REF
Aerated lagoons Should be lined with clay or some natural source, 1.8 – 6 m depth, 10-30 day retention
time, oxygen supplied by additional mechanical means
BOD removal of up to 95%
Low cost, low maintenance and energy requirements, can be well
integrated into surrounding landscapes, reliable treatment even
at high loads,
Nutrient removal is less efficient due to short retention times
USEPA, (2002) FUCHS, (2011)
FIXED FILM SYSTEMS Conventional
biofilters (trickling filters)
Bed with supportive media such as stones, plastic, wood; 0.9 – 2.4 m deep; oxygen
supplied via natural flow of air;
BOD Removal of between 80 - 90%
Low land requirement Moderate level of skill required for
operation and maintenance Suitable for small to medium
communities
Accumulation of excess biomass will affect performance; high level
of clogging thus regular backwashing is required; if suddenly shut down – anaerobic conditions result in reduced effluent
quality; odour and snail problems
Chaudhary et al.
(2003);
USEPA (2000)
Rotating biological contactors
High contact time; high effluent quality; resistant to shock hydraulic
or organic loading; short contact periods; large active surface area;
silent; low sludge production; easy transfer of oxygen from air;
Continuous power supply required;
oxygen may be a limiting substrate;
Kadu and Rao (2012)
Biological aerated filters
Consists of a reactor container, media for supporting biofilm growth, influent distribution and effluent collection system;
Optimal conditions – pH 6.5 – 7.5 with mixing; Media should be chemically stable, high surface area and low weight eg: sunken
clay, floating polystyrene beads, pure polypropylene
High nutrient removal (80 – 100%)
Environmental factors such as pH, temperature will aid microbial growth; high bacterial and nutrient removal efficiencies; can combine
ammonia oxidation and solids removal in a a single unit
Media may become clogged due to biomass growth and accumulation –
may create resistance to air and flow of liquid; regular back washing is required to remove
excess biomass and particles
Mendoza- Espinosa and
Stephenson (1999); Asiedu
(2001)
11 1.3.4 Tertiary treatment
Tertiary treatment generally follows secondary treatment and aids the removal of those wastewater constituents and pathogenic microorganisms such as faecal coliforms, streptococci, Salmonella sp. and enteric viruses that were not removed by previous treatments (SOPAC, 1999). Disinfection or tertiary treatment may be divided into three main categories i.e., chemical, physical and irradiation. Physical treatments generally involve one or a combination of treatments such as rapid sand filtration, nitrification, denitrification or carbon adsorption which is employed prior to chlorintion to remove any remaining suspended solids as well as reduce the amount of nitrates, phosphates and soluble organic matter present.
Following this, disinfection by chemicals and irradiation may occur and generally involves one or a combination of treatments involving chlorination and ultra violet light exposure or ozonation, the choice of which depends solely on the incoming effluent quality, ease and cost of installation, maintenance and operation as well as the effects on flora and fauna. The disinfection processes commonly used are discussed below:
1.3.4.1 Chlorination
Chemical oxidation processes include ozone, hydrogen peroxide and chlorine which may be applied in various forms such as pure chlorine, chlorine dioxide or chlorine compounds such as calcium hypochlorite or sodium hypochlorite. The major factors that need to be taken into consideration when evaluating the performance of chemical disinfectants are contact time, efficiency of mixing, type and concentration of chemicals used, residual remaining, pH and the concentration of interfering substances which may reduce the effectiveness of the disinfectant (USEPA, 1999c). Chlorination is the commonly used treatment for disinfection
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of surface and groundwater sources, reacting with any form of organic matter that may be present in previously treated effluent (EPA, 1997). Chlorine gas is a strong oxidant that is most commonly used in larger treatment plants since it is more cost effective than other methods of tertiary treatment as well as allowing for easy and accurate application. Chlorine dioxide is a powerful oxidant that is capable of oxidising iron and manganese as well as removing any colour components in the effluent. It is generally prepared on-site and is one of the most economical methods available. Calcium hypochloride, also known as high test hypochlorite is available in the form of granules, powder and tablets whilst sodium hypochlorite, also known as household bleach is a 13% solution of chlorine which is equivalent to 10 - 12.2% available chlorine (USEPA, 1999c). This compound however is extremely unstable and deteriorates rapidly. When elemental chlorine comes into contact with water, it is hydrolysed to hypochlorous acid (HOCl) and hypochlorite (-OCl), with HOCl being one of the strongest disinfecting agents. In addition, chlorine also reacts with ammonia to produce a range of mono- and dichloramines which serve as less potent disinfectants.
NH3 + HOCl → NH2Cl + H2O (monochloramine)
NH2Cl + HOCl → NHCl2 + H2O (dichloramine)
NH2Cl2 + HOCl → NCl3 + H2O (nitrogen trichloride)
One of the major disadvantages, however, associated with chlorination is the production of toxic byproducts such as trichloromethanes and other chloramines which cause severe harmful effects on the receiving water bodies into which they are discharged (Gross and Farrell-Poe, 2004).
13 1.3.4.2 Ultraviolet light
The use of ultraviolet light as a means of disinfection involves the use of electromagnetic energy from a mercury arc lamp to irradiate and disinfect wastewater effluent. The efficiency of this disinfection method depends on the dose as well as achieving an optimal wavelength range between 250 – 270 nm. In addition, a range of factors have to be taken into consideration such as effluent quality, UV light intensity, path length from the source lamp to the respective pathogenic microorganisms as well as exposure time (USEPA, 1999b). The UV light penetrates the cell wall of exposed microorganisms, ultimately damaging their genetic material and preventing survival. However, often when UV is applied at lower doses, microorganisms tend to reverse the damage through their own cell repair mechanisms (SYRIA; USEPA, 2004). In addition, routine cleaning of the arc lamp should be conducted due to the large amount of interference that may occur from chemical components present in the wastewater being treated.
1.3.4.3 Ozonation
Ozone is a highly reactive, unstable gas that is generally used as a disinfectant and does not leave any residual behind, reacting with any organic matter present within the wastewater.
O2 + energy → O + O, then O + O2 → O3
Due to its unstable nature, it must often be generated onsite in ozone generators by the passage of oxygen through a high voltage electric field. The required ozone dosage is dependant on a range of factors, the most important being type of effluent being treated. In
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addition, other competing reactions within the water environment may also contribute to the overall ozone demand. Previous studies have shown ozone requirements ranging between a few mg/l to greater than 10 mg/l for primary effluent (Lazarova et al., 1999). Ozone is generally used as it results in the elimination of any odours, does not result in any residual compounds, can be easily generated from air thus resulting in the process being entirely dependent on the available power source. However, the major disadvantages include the high costs involved (USEPA, 1999a).
1.3.5 Nutrient removal
Tertiary treatments involving nutrient removal are often referred to as advanced methods of wastewater treatment and usually occur after or in conjunction with conventional biological secondary treatment to aid both nitrogen and phosphorous removal from wastewater.
Generally these methods may include some form of physical or chemical technique such as flocculation, precipitation or membrane filtration. Two such commonly used techniques include Biological Nutrient Removal (BNR) and the Enhanced Nutrient Removal (ENR) which serves as a modification of the suspended growth treatment systems, achieving nitrogen and phosphorous removals of 8 - 10 mg/l; 1 – 3 mg/l and 3 mg/l; 0.3mg/l per respective process (Hartman and Cleland, 2007). Wastewater containing nitrogen is generally present in the form of ammonia and is not usually removed by prior conventional secondary treatments. Therefore, the advanced treatment methods successfully aid in the conversion of ammonia and other organic forms via nitrification and denitrification to non-toxic nitrate and subsequently nitrogen gas. Generally secondary biological treatment processes achieve phosphorous removal rates of less than 20%, requiring the need for additional removal methods. Physical precipitation such as filtration techniques as well as chemical precipitation
15
such as flocculation after lime or alum addition may occur which aids in achieving phosphorous reduction rates of up to 95%.
1.4 Effect of improperly treated wastewater effluent
1.4.1 Effect on the environment, micro- and macrofauna
The biggest concern associated with microbial pollution is the risk of human and livestock related illnesses after exposure to contaminated water sources. Often the discharge of improperly treated effluent from WWTPs results in the deposition of large amounts of organic matter and nutrients which has major detrimental effects on the surrounding environments as well on the micro- and macro-fauna present. Excessive nutrient loading can lead to eutrophication and temporary oxygen deficiencies that ultimately alter the energy relationship and water balance, disrupting biotic community structure and function.
Excessively turbid effluent discharge can also result in the deposition of sand and grit into the aquatic system ultimately disrupting sediment characteristics and hindering natural water flows (Wakelin et al., 2008). In addition, the overall hydrological and physicochemical environment is often affected due to the discharge of improperly treated effluent with many of the micro- and macro- fauna within these water bodies exhibiting distinct physiological tolerance levels. Disturbances to the overall environment can severely affect those intolerant individuals either in the form of adverse behavioural characteristics or more severely in the form of death. Often death decreases a large degree of resource competition and predation within the environment thereby resulting in the proliferation of tolerant organisms. This ultimately causes an imbalance amongst the group of organisms present and the overall alterations to the surrounding environment in the form of nutrient modifications, light and
16
oxygen content, food sources as well as habitat loss (Coetzee, 2003). In addition, the deposition of excessive nutrients leads to profuse plant growth along river banks which in certain cases may be visually pleasing but may serve as a health hazard due to entanglement.
In addition, benthic microbial and algal growth may cause rock and wood surfaces to become slippery, posing a threat to human safety.
1.4.2 Effect on human health
Communities situated downstream or close to municipal sewage outfalls or contaminated water sources are at the highest risk of illness due to increased microbial pathogens and deteriorating physicochemical parameters (Wakelin et al., 2008). Often the discharge of extremely turbid effluent in conjunction with dense algal blooms results in poor visibility within these water bodies resulting in submerged hazards not being visible thus creating dangerous situations for recreational users. In addition, water bodies used for full contact recreational activities may serve as a source of a wide range of infectious diseases which may be contracted either by ingestion of contaminated water or through full body contact (DWAF, 1996b). However, depending on the type of waterborne disease and on the physical health of the individual concerned, the person may either recover completely from the resultant disease or suffer permanently. In addition, a variety of skin and ear infections may arise as a result of contaminated waters coming into contact with broken skin or penetration of the ear. The discharge of improperly treated effluent often results in increased number of bacterial, viral and protozoan pathogens which may result in a range of waterborne related diseases such as gastroenteritis and infections of the ear, nose and throat (Okoh et al., 2010). A number of indirect health hazards such as chemical contaminants, disease-transmitting organisms, such as mosquitos and fresh water snails implicated in malaria and bilharzia may also arise
17
depending on the state of the surface water source, leading to other additional human health hazards (Coetzee, 2003).
1.5 Methods of effluent disposal
The type of wastewater treatment chosen per plant will depend solely on the incoming waste as well as where the treated effluent will be discharged. The discharge of waste is grouped into two main categories, based on the spatial nature of the waste source namely, point and diffuse source with the latter initially being discharged as a point source, after which it migrates towards the water resource and has a diffuse impact (DWAF, 2003). The actual destination of discharges is important because it largely determines the extent and nature of the impact. In addition, the waste volume may also disturb natural cycles in receiving water bodies such as rivers ultimately affecting not only the water quality but also water flow. For larger municipalities located near coastlines, an additional option exists to discharge treated effluent into the ocean whereby oceanic processes can be used to reduce effluent contaminant concentrations to the required guidelines for recreational purposes and to comply with environmental standards (DWA, 2011). In addition, due to the constant changing physical conditions along South African coastlines, responsible disposal of wastewater to the marine environment is considerably allowed due to the reduction of concentrations brought about by the initial dilution of the effluent, the dispersion of the effluent plume and the decay of microorganisms. In addition, depending on the type of effluent, the surrounding areas, state of the coastline and the degree of dilution that can be achieved after oceanic discharge, the wastewater may require different degrees of pre-treatment prior to discharge (Table 1.2).
Within the eThekwini Municipality itself, two major wastewater treatment works, namely The Central Works and Southern Works both discharge effluent into the Indian Ocean.
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Within these plants, initial influent is subjected to conventional screening, de-gritting and primary sedimentation followed by subsequent discharge to the sea via outfall pipes.
Table 1.2: Overview of treatment requirements for selected effluent discharges
DESTINATION PRELIMINARY PRIMARY SECONDARY TERTIARY IRRIGATION
Produce eaten raw YES YES YES YES
Other produce YES YES YES NO
GROUNDWATER YES YES YES YES
SURFACE WATERS YES YES YES NO
SEA OUTFALLS YES YES YES NO
Adapted from USEPA (2012)
1.6 Commonly detected microbial indicators in treated wastewater effluent and associated infections
The WHO estimates that globally, approximately 1.1 billion people consume unsafe water with approximately 88% of diarrhoeal diseases and 1.7 million deaths being attributable to unsafe water, sanitation and hygiene (WHO, 2008). Microbiological examination and monitoring is commonly used worldwide to ensure the safety of a range of water sources whereby contamination with human and animal excreta could pose serious risks. Many potential pathogens (Table 1.3) could be associated with contaminated water however, it is both time consuming and expensive to test for all possible pathogens present. Hence,
